1. Field of the Invention
The present invention relates to a valve having a mechanism to enable change between supply and discharge of air, in particular, relates to an energy-saving valve having a decompression mechanism which enables the pressure of compressed air to be reduced and the compressed air to be discharged from a discharging port.
2. Description of the Related Art
In typical air cylinders which have been widely used as pneumatic actuators in various types of automatic machines, a piston having a fixed rod reciprocates in a process in which compressed air is supplied into a pressure chamber and the compressed air is then discharged from the pressure chamber. In general, air is supplied to and discharged from air cylinders by a diverter valve.
In such air cylinders, although a working stroke which contributes to works in the reciprocation of a piston needs large driving force because external loads are imposed on a rod in the working stroke, a return stroke in which the piston returns to the initial position needs driving force smaller than that in a working stroke because external loads are not imposed on the rod. The driving force depends on the magnitude of the pressure of compressed air supplied into a pressure chamber. In view of energy conservation and reduction of the running cost by saving air consumption, the pressure of compressed air supplied into a pressure chamber in a return stroke is preferably smaller than that in a working stroke.
In consideration of such an issue, Japanese Unexamined Patent Application Publication No. 2002-013504 has proposed a technique in which pressure-reducing valves 6 and 125 are provided in a main channel connected to pressure action chambers of a cylinder tube. However, since the pressure-reducing valves 6 and 125 need to be provided in addition to a valve which enables air to be selectively supplied into and discharged from the pressure action chambers of the cylinder tube, equipment becomes complicated and large, which leads to the increase of the initial cost.
The inventors of the present invention have proposed a technique in Japanese Patent Application No. 2010-27943, which imparts a simple structure and small size to a valve which enables the pressure of compressed air supplied into a pressure chamber to be small in a return stroke as compared with a working stroke. However, more simple structures have been demanded.